           (and (= x-dist 0) (> y-dist 0)) :up
           (and (= x-dist 0) (< y-dist 0)) :down)))
 
-(defn move-zombie [terrain current-pos action]
+(defn- move-zombie [terrain current-pos action]
   (let [new-pos (get-position current-pos action)]
     (if (terrain-accessible? terrain new-pos)
       (clojure.set/rename-keys terrain {current-pos new-pos})

(defn zombie-health [game position]
  (:health (get-in game [:terrain position])))

(defn is-zombie? [terrain]
  (= (:type terrain) :zombie))

(defn zombie-positions [game]

                   []
                   (:terrain game))))

(defn- calculate-zombie-action [[x y] [player-x player-y]]
  (let [x-dist (- x player-x)
        y-dist (- y player-y)]
    (cond (and (> x-dist 0) (> y-dist 0)) :up-left
